Manufacture of ddt



Patented Oct. 6, 1953 UNITED STATES PATENT OFFICE MANUFACTURE OF DDT LeoP. Curtin, Cranbury, N. J.

No Drawing. Application July 3, 1951, Serial No. 235,091

4 Claims.

This invention relates to manufacture of DDT; and it comprises a methodof producing 1,1,1- trichlor 2,2-bis(p-chlorophenyl)ethane, commonlycalled DDT, wherein chloral and chlorobenzene are mixed with strongsulfuric acid; this mixture being agitated and maintained attemperatures within the range of about 10 to +25 C. while oleum isslowly introduced over a period of from about 40 to 90 minutes or more,the time depending on the efiiciency of the removal of the heat ofreaction; sufficient oleum being added to supply from about 0.5 to 1.3moles of free S03 in the reaction mixture in addition to any required tobring the sulfuric acid to a concentration of 100 per cent H2804;sufficient chlorobenzene being added at least before the addition ofoleum is completed to supply a total of from about 2.2 to 4.0 moles to 1mole of chloral; a catalyst being also added to the reaction mixture inaddition to any present in any recycled spent acid; said catalyst beingan aromatic polysulfonic acid which is soluble in but substantiallynon-reactive towards the reaction mixture, the total quantity ofcatalyst present in the reaction zone at the start of the processamounting to from about 5 to 60 per cent by weight based on the weightof the chloral; the reaction mixture being agitated for a period of fromabout 1 to 6 hours, depending on the temperature used, until thereaction is complete, after which the DDT, which precipitates in theform of finely-divided, fiuffy white crystals, is separated from thereaction mass, either by filtering or centrifuging or by solventextraction; all as more fully hereinafter set forth and as claimed.

The commercial manufacture of DDT is a rather recent development.Several diiferent methods of manufacturing this important insecticidehave been described in the literature. Most of these methods involve thecondensation of 1 mole of chloral with two moles of chlorobenzene in asulfuric acid medium. In all of these methods with which I am familiaran excess of chlorobenzene is present in the reaction zone throughoutthe process and the DDT is recovered either in the form of gummyspheroidal masses ranging from the size of a pea to that of an orange orin the form of a molten mass. In both cases the recovered DDT containsquantities of unreacted chlorobenzene which can be eliminated only withconsiderable difficulty. The resulting products are so gummy that theycannot be ground at ordinary temperatures and it has therefore becomeconventional to grind them in the presence of solid carbon dioxide whena finely-divided product of high setting point is required. It is alsotrue that the products produced in this fashion contain only from about70 to 76 per cent of 1,1,1-trichlor-2,2-bis(pchlorophenyl) ethane. Theprincipal impurity is 1,1,1 trichlor 2 o chlorphenyl-Q-p-chlorphenylethane, commonly known as ortho-para DDT. This material has relativelylittle insecticidal value but is present in proportions of 20 per cent,more or less, besides 5 per cent or more of a miscellaneous collectionof impurities of which about 15 have been identified. The purity of thisproduct is usually determined by making a setting point determination. Asetting point is obtained rather than a melting point because of thehigh percentage of impurities in the commercial material... Nearly allcommercial DDT is sold with a guaranteed minimum setting point of 89C.-a Government specification.

I have discovered a method of making DDT which eliminates most of thedifiiculties mentioned above. In this method-J believe for the firsttime-a crystalline product is obtained which is sufficiently fine formost purposes. And this product can be ground, if desired, without theuse of solid carbon dioxide. The product obtained analyzes from about 83to 88 per cent of para-para DDT which means that the impurities presentin the usual commercial product have been reduced by about to per cent.In ad dition this process results in a substantial saving of time. Thisprocess may be described briefly as follows:

A jacketed reaction vessel provided with an agitator is employed with arefrigerant flowing through the jacket at a rate suificient to keep thetemperature preferably within the range of from 2 to +2. C. during thereaction. Strong sulfuric acid is first introduced into the vessel. Ifthe process has been conducted previously this acid may be the spentacid from the prior run and may amount to from about 30 to per cent(preterably from 30 to 50 per cent) of the total spent acid recovered inthe prior run. This acid is of value primarily as a diluent; it is spentso far as the reaction is concerned. The catalyst, more fully describedbelow, the chloral to be used in the process and the chlorobenzene areadded to the acid in the reaction vessel.

As soon as the batch has reached the desired low temperature thereaction is started by the addition of oleum while the batch is beingagitated.- I have found that the free S03 in the oleum acts as thecondensation agent and that the rate of reaction can be controlled bythe rate 3 of its addition. From about 0.5 to 1.3 moles of free S03 mustbe supplied per mole of chloral in addition to any required to bring thesulfuric acid up to a concentration of 100 per cent H2804. The optimumquantity of S03 to be added after the sulfuric acid is brought up to 100per cent strength is about 1 mole S03 per mole of chloral plus fromabout 3 to per cent additionalgto allow for that consumed by'sidereactions. The oleum may contain'from about 10 to 65 per cent freeSO3-preferably -30 per cent-and it should be added slowly over a periodof from about to 90 minutes. The reaction mixture is then advantageouslystirred for an additional two to four hours. The temperature may beallowed to rise slowly in this-stirring period to a temperature, at thefinish, of 10 to 15 C. The reaction mixture when produced as abovedescribed, is a magma of fine fluffy crystals of DDT and these can bereadily removed by a centrifuge or filtered ofi,=then washed withwaterand dried. Or, the crystals :can be dissolved in a water-immiscibleorganic .solvent and there- -sulting solution separated from the acidic"lower layer.

The filtrate obtained after the-crystalsof DDT are separated is a goldenor amber colored spent acid which in addition to sulfuric and sulfonicacids, contains from zero to three "percent of water. The lower thetemperature used in the process, the purer the spentacid obtained. Whenreaction temperatures above about '11" C. are employed the spent acid istooimpure to be advantageously cycled. For this reason I .usually preferto employ reaction temperatures n'ot substantially exceeding 11 C.

If it is preferred to employ solvent extraction to separate the crystalsof DDT from the reaction mass, a low-boiling water-immiscible organicsolvent is used. This solvent must be, of course, substantially inerttoward the reaction components. Any solvent for'DDT which fulfills theseconditions is suitable. Examples are petroleum fractions boiling betweenabout to 100 C. which may contain substantial proportions ofcycloparaffins and/or aromatics, carbon tetrachloride andtrichloreth-ylene.

It should be noted that the spent acid obtained from other DDT processesis-a dark, foul mate rial containing tars and many other impurities inhigh concentration. The industry conventionally either discards it orincinerates it to recover oxides of sulfur therefrom.

The crystalline product obtained as-above'described contains from 84 to87 per cent of parapara DDT more or less and has a setting point about965 C. or higher. And it is not even necessary to grind the product forordinary purposes. 'If a very fine dusting powder isdesired, however, itis only necessary to mix the crystals with an inert mineral filler, suchas talc, followed by grinding. It is entirely feasible, however, tomeltthe DDT prepared by my process and thus effect a separation "fromwater and water soluble materials.

I believe that the DDT is precipitated 'inmy process in the form offinelyedivided crystals for the reason that the product is muchpurer'than the products produced in other processes. The catalystsappear to be largelyresponsible for the purity of my product since theyhave what'might be called a para-directive effect in causing theformation of the para-para compound at the expense of the ortho-paracompound. This. in in addition to the accelerating effect the catpresentin the reaction zone. The total quantity of catalyst present in thereaction zone should be from about 5 to 60 per cent by weight based onthe weight of the chloral. Part of the catalyst presentmay be derivedfrom the recycled spent acid, since the catalyst remains substantiallystable during the reaction. If spent acid is not employed in the processit is necessary, of course, to add the entire quantity of catalyst tothe reaction mixture and I have found, surprisingly, that a minimum ofabout 5 per cent of catalyst must be employed based on the weight of thechloral in order to produce any appreciable=ef fect upon the process.The requirement of such a large quantity of catalyst is surprising inview of the fact that in most organic processes the amount of catalystrequired is often only 1 .per cent or less. Even if'spent acid isemployed containing catalyst it is necessary to add at least about 3 percent of catalyst separately to the reaction zone owing to the fact thata'substantial proportion of the amount'originally present in thereaction zone is lostiin the spent acid that is not recycled. Thequantity of catalyst required in the reaction zone varies considerablywith .the activity of the catalyst and with some relatively inactivecatalysts it requires up to about '60 per cent by weight based on theweight .ofthe chloral. An excess of catalyst over the'minimum requiredusually does no harm but is merely wasted.

I have discovered that the activity of my catalysts depends uponthenumberof sulfonic groups they contain and also upon the type ofsubstituent groups present in the aromatic part of the molecules. Forsatisfactory catalytic performance the catalysts should contain two .ormore sulfonic groups'and the catalytic activity is enhanced by thepresence of positive substituents in the organic radical, that is,substituents such as halogeno, 'nitro, cyano, carboxy, carbonyl,sulfonic groups etc. These groups enhance the acid'properties of thecompounds, i. e. they increase their ionization. Negative 'substituents,such as amino, hydroxyl or alkyl, may be present but these eitherdecrease the catalytic activity or produce substantially no effectthereon.

Examples of the catalysts which are operative in my process are-.Benzene-l,3-disulfonic acid Diphenylmethane-2,4,2',4'-tetrasulfonicacid Quinoline-5,7-disulfonic acid Anthracene-1,5-disulfonic acid It isevident, of course, that many of the catalysts in the above list aremerely of academic interest owing to their high cost. Some of the abovecompounds are slightly reactive in the reaction mixture and for thisreason are not advantageous as the inert catalysts.

Cost, efiiciency and ease of manufacture considered, it is probable thatchloro benzene-2,4- disulfonic acid is the most advantageous catalyst touse. l,2-dichlorobenzene-.'-3,5-disulfonic acid is a probable secondchoice. To show the effect of negative substituents upon the efficiencyof the catalysts it may be mentioned that xylene disulfonic acid is onlyabout 60 per cent as efficlent as 1,3-benzene disulfonic acid inaccelerating the reaction. Halo substituents in the benzene nucleussubstantially increase the efficiency of the catalysts.

Many of the catalysts listed may be manufactured conveniently and at lowcost. For example, in the production of 1 chloro 2,4-disulfonic acid,the following procedure is very satisfactory:

Parts by weight 1) is placed in a jacketed vessel, equipped with astirrer and with very strong cooling, about half of (2) is run in over aperiod of 40 to 50 minutes, depending on the efficiency of the cooling.The monosulfonation is very exothermal. The best temperature for themonosulfonation is below 30 C., a range of 20 to 30 being satisfactory,although sulfonation takes place below C. The product is now a liquidwhich is almost colorless, usually clear with a faint pinkish-ambertint. It may solidify to a mass of fine white crystals at this point ifnot heated promptly. The crystals remelt at about 70 C. The mixture isheated to about 130 C. and the remainder of (2) is run in over about 20minutes as the second sulfonation is only slightly exothermal. Themixture is maintained at 160 C'. to 190 C. for about 30 minutes, cooledsomewhat and (3) added to destroy a little free S03 remaining. Theproduct is a syrupy golden amber liquid containing about '70 per cent ofthe desired catalyst and this reaction mixture may be added to the DDTsynthesis without further processing. The catalyst in example1,1,2-dichlorobenzene- 3,5-disulfonic acid, may be made by a similarprocedure except that the final temperature is 170-200 C.

Chlorobenzene-2/l-disulfonic acid may be made at remarkably low cost,utilizing the p-chlorobenzene sulfonic acid present as a byproduct inthe spent acid. The latter is highly soluble in water and also in strongsulfuric acid. If however to the spend acid about percent by weight ofwater or ice is added and the mixture cooled, the p-ohlorobenzenesulfonic acid precipitates out almost quantitatively in the form of finecrystals, ivory white to white in color.

A quantity of this precipitate containing 192.5 parts by weight ofp-chlorobenzene sulfonic acid, is placed in a reaction vessel and 160parts by weight of 65% oleum is added and the mixture is heated to andmaintained at 160 C. for 30 to 60 minutes. The reaction mixturedissolves to a clear, homogeneous solution, sulfonation takes placemostly above 130 close to quantitative. 100 parts by weight of sulfuricacid, 5. g. 1.84 is added. This 11 eutralizes the excess sulfur trioxideand converts the viscous reaction product into a much more fluid, easilyhandled material. This product can be used directly as a catalystwithout further processing. If heated much above 200 C. say, to 300 C.,a substantial part of the 1,2,4 compound rearranges to the symmetrical1,3,5-trichlorobenzene disulfonic acid. This is a good catalyst but notquite equal to the 1,2,4 compound.

The spent acid recovered in my process contains, aside from the catalystadded in the process, small proportions of various sulfonic acids, suchas ortho-para and para-para DDT sulfonic acids, mono-chlorobenzenesulfonic acid and various other sulfonated byproducts formed in thereaction. These compounds may produce some catalytic action when thespent acid is recycled. But in no case have I found it possible toobtain satisfactory results in my process by relying solely upon thecatalysts present in the recycled spent acid, It is usually necessary toadd at least about 3 percent of catalyst in addition to anyautomatically recycled in the spent acid.

The water washing step of my process is advantageously conducted incounter-current and is highly effective owing to the crystalline natureof the DDT. If the washing step is done with care, the resulting productis 100 percent soluble in organic solvents. If 10 grams are warmedslightly with 100 grams of Stoddard solvent, for example, the DDTdissolves completely and cleanly, with no trace of residue. On coolingto 15 C. no change takes place. If the DDT contains a trace of moisture,say 0.01 percent, the solution in the petroleum solvent may develop afaint opalesence but nothing more.

Water washing also eliminates the acid from my product. The presentcommercial product usually contains free acid which has causedconsiderable difiiculties due to corrosion of spray apparatus. That theproduct produced by my process is free from acid can be demonstrated bystirring 10 grams in 10 cc. of tap water. In one such test I found thatthe tap water had a pH of 6.5 and after stirring in the DDT it remainedat this value for 48 hours. The mixture was then heated to boiling whichmelted the DDT. But after cooling the pH of the mixture was still 6.5.

It has been mentioned that the preferred reaction temperature for thepresent process is in the neighborhood of -2 to +2 C. It will operate ofcourse at 15 C. and above although, with the catalyst used, the reactionis decidedly vigorous at such temperatures. It also proceeds well at -30(2., the reaction at that temperature being almost 50 percent as rapidas at 0 C. I have studied this reaction with disulfonic acid catalystsfrom +40 C. to 30 C. and find that decreasing the temperature increasesthe proportion of para-para DDT in the product. The reaction temperaturerecommended, 2 to +2 C. is a compromise. The action is as fast asconvenient at that temperature, the physical form of the DDT is mostdesirable, the setting point C. and the reaction is of the product isunprecedentedly high, no tars,

or other colored products are formed, the reclaimed acid is clean andthe yield excellent.

The following examples will illustrate the process. In all cases, thefuming acid is added at a fairly uniform rate over a period of 45 tominutes or more.

acumen:

Exampleti Parts'by weight- ('1'). Chloral anhydrous; 147.4: (2)Chlorobenzene 295' (3) Catalyst, 1",2-dichlorob'enzene-2,5 disul'fonicacid; 3'0 (4) Sulfuric acid fuming; 2l.5% free S03" H810? ('5) Spentacid from preceding batch"--- 55010" Items (5), (3), (1 and (2)are-first added, usually in the order given; to a reaction kettle;jacketedand equipped with e'fiicient stirring apparatus; After startingthe stirrer and bringing" the mixture to a 6. or a little belowbymeansof brine or other cooling medium" circulating in the' jacket, theaddition or (4) is commenced; This is completed" in eliminates,thetemperature being maintained at -1 to +2 C1 approxi-" mately, at alltimes. After the reaction iscomplete, the reaction mass, now a thickmagmaof crystalline particles of'DDT in" a mother liqnor of spent acid,is stir-red for an additional two hours then" dumped intoa receivingvessel. The reaction kettle is now ready to receive another batch. Thereaction mass is therr filtered or centrifuged, washed thoroughly withcold water and dried. The product; is nowi'n suitable form for sale orconversion into" insecticidal formulations'. The yield of DDT, based on"the chloral, is 94 percent of theory This product has a settingv pointof 95.5" C.

Example 2' Parts-by weight.

Example 3' Parts by: weight (1)" Chl'oral' T455 (2') Chlorob'enzen'e-2'95 (3.) Catalyst, benezene-1',3'-dis lfo'nic acid 65: (4) Sulfuricacid; fuming 20% free S05-.. 445 (5') Sulfuric acid 99% 500 This exampleillustrates-one method" or start ing a series of runs whereno spent acidfrom a previous operation is available.- Bhe usual spentacid in" thiscase is replaced bya 99' percent Sui-- furic acid and it'is necessarytoaddfrom about 50 to- 100 percent more catalyst owing'tothe fact thatnone is. present inthe acidused in theproo es's. It is possible, ofcourse" to utilize strong sulfuric acid ranging in strengthf'rcm about-90 to 100 percentbut it is usually lessexpensive toutilizean acid havinga concentration. close. to: 100- percentsince ifan: acid of lowerstrength isemployed this requires the addition on more. fuming acid or.a fuming acid of higher. s03: content.

- stirring? period 1- 5 hours.

parts: of:

In conducting, this run the procedure: used: is: substantially thatusedin Examplealbutthe temperature is maintained between 5'-7 G. The"addition period is 55 minutes and the subsequent A DDT having a setpointof 935 C. is obtained ina yield of ab out9320 percent leased on thechloral";

Example: 4-

Parts by weigh (1') Chlorall 147.4 (2) Chl'orobenzene 290 (3:). CatalystdiphenyL- 21454. trisul'fonic acidl Sulfuric acid}, 21.5%. free S03.416i (5 Spent. acid from preceding. batches.. 550T Same procedure usedas in Example- 1 The DDT has a setting point of 9'4? andtheyield isabout 92 percent;

Ewample 5 The. procedure used' is the same. as that of Ex.- ample: 1except. that the catalyst. employed is 24.

benzene-1,3,5-trisulfonic acid. An addition time of 45 minutes is usedand the subsequent stirringsp'eriod is 90 minutes. DDT setting point.94.5" yield 92 percent.

Example 6" The procedure used is the same as that of Example 1 exceptthat the catalyst' employed is 35* parts of quinoline-5fl-di'sul'fonicacidi An addition time of minutes" is used and the-subseuuent' stirringperiod 95 minutes. DDT setting: point 94 yield 19 percent.

Example 7? The procedure-'used isthe same as -that or-.Ex--- ample Iexc'ept-thatthe catalyst employed i's 53 parts ofanthracene-1;5-disulfonic acid. DDT setting point 94 yield percent.

Example 8. Same procedureas in.Exa'mple- 2; except that the: catalyst is45 parts or: diphenylmethanex-ZAL.

ZAJ-tetrasulfonic acid: DDT setting point. 94 yield 90 percent.

Example 9.

Same procedure as in Example 2; except for the finishing of the batch.After the reaction is complete 200' grams monoehlorobenzene is added"toassist in separating the DDT from the spent acid, which nowiorms awelt-defined lower layer- This" is drawn on; andv the organic layer iswashed free of acid. It is then steam distilled toremove allchlorobenzene present. The DDT, now molten, forms a heavy lower layerand this is drawn off; A small amount of emulsified water is vaporizedand the melted; anhydrous DDT is flaked or cast into cakes; Yield93:7%-; S. P. 9518" C:

An extensive series of additional runs have been'mad'e' with slightvariations intheproc'edure described utilizing various aromaticpolysulfonic acids as cataiyst and with theproductionor'DDT productshaving settingipoints within: the range of. about 92$*-9&? in yieldsranging from about 9.1 to 95' percent of; theory based on the weight ofthe: chloral. My'conclusion, that all aromatic polysulfonie acids areuseful as catalysts in myprocess which are soluble in and substantiallyinert towardthe: sulfuric acid reaction medium,-

75 13; median. these extensive testsc The advantages obtained by myprocess can be summarized as follows:

1. A lower manufacturing cost, due to reduced time of reaction and useof recycled spent acid.

2. Higher rate of production.

3. Greatly simplified finishing procedure.

4. Excellent physical form obtained without special treatment.

5. Elimination of oil-insoluble residues.

6. Production of a spent acid having commer cial value.

7. A purer product having a higher setting point, an unequaled highcontent of para-para DDT and less impurities.

While I have described what I consider to he the most advantageousembodiments of my proc" ess it is evident of course that variousmodifications can be made in the specific procedures which have beendescribed without departing from the purview of this invention. I havealready mentioned the fact that the spent acid obtained in my process isa relatively pure product substantially free from tarry matter. For thisreason it is possible to utilize the acid which is not recycled forvarious purposes for which the spent acid derived from other processeswould not be at all suitable. Thus my spent acid can be neutralized withammonia to form a commercial ammonium sulfate suitable for use as afertilizer. production of precipitated barium sulfate and lead sulfate,as well as soluble sulfates, such as aluminum sulfate. This is incontrast to the serious trouble experienced by manufacturers of DDTusing other processes to get rid of their waste acid. It is impossibleto dispose of such acid by passing it directly into streams or harborsand some manufacturers have even been forced to purchase soda ash toneutralize it.

The quantities of chloral utilized in the foregoing specific examplesare based on anhydrous chloral. It is possible, of course, to employchloral in other forms, for example, as chloral hydrate, provided thatthe necessary increase in added sulfur trioxide is made.

As indicated previously the total quantity of catalyst in the reactionzone at the start of the process required to produce satisfactoryresults in my process depends in an important degree upon itseffectiveness or activity in promoting the reaction and upon itspara-para directiveness. The best of the catalysts which I have testedproduce an appreciable effect when present in the reaction zone in totalquantities amounting to only from about to 10 percent of the chloral byweight, whereas some of the inferior catalysts should be present inquanti ties up to about 50 to 60 percent based on the weight of thechloral. In the above specific examples from about to percent ofcatalyst is added separately to the reaction mixture, not including thecatalyst which is present in the recycled spent acid. The amount ofspent acid which can be recycled depends, of course, upon the strengthof the oleum used in the process. If a 65 percent oleum is usedapproximately 60 percent of the spent acid can be recycled and this, ofcourse, will usually contain approximately 60 percent of the catalystoriginally present in the reaction zone. When a 20-30 percent oleum isused the amount of spent acid recycled may amount to from about 30 to 50percent of the total. If an expensive catalyst is used it may be cheaperto use a 65 percent oleum so that less catalyst is lost in the spentacid. It is I The acid can also be used in the i possible, of course, torecover catalyst from the spent acid which is not recycled. This wouldnot be difficult but in general would not be profitable, since severalof the catalysts which are highly active in the process are alsorelatively inexpensive.

One of the most important features of the process for making DDT whichis herein de-- scribed is that it permits of the production of purepara-para DDT without the necessity of producing, simultaneously, largequantities of an unsaleable byproduct. As stated above, the joint Armyand Navy specification for DDT requires a setting point of,89.0 (3.,minimum. This corresponds roughly to a para-para DDT content of 73.8percent although there are some products which meet the setting pointspecification but which have as little as 71 percent para-para DDT.

It is evident that, if even a small amount of the para-para DDT contentwere removed from such material, the remainder would not meet anyexisting specification and would be not only unsaleable but a nuisance,as well. Such is not the case with the improved DDT herein described.

Consider a DDT made in accordance with Example 2, With1-chloro-2A-benzene dlisulfonic acid as the catalyst. Such a material,containing 85 percent or more of para-para DDT and 15 percent or less ofimpurities, is dissolved in a hot petroleum fraction in which it isextremely soluble. With a proper choice of temperatures andconcentration, on cooling, parts of parapara DDT will crystallize out inthe form of beautiful pure white needles. This precipitate is washedwith a little cold solvent, which is added to the next batch. Theproduct is a 99.3 to 99.9 percent para-para DDT. The mother liquorretains all of the impurities, 15 parts, and the remainder of thepara-para DDT, l5 parts. It will be noted that this is a solution of a'75 percent para-para DDT, a better than average material, which meetsspecifications and may be sold '11 solution form, for which there is avery large market, or recovered as a solid by evaporating the solution.The 99.3--9 percent product has been tested and found, in comparisonwith a 89 C. setting point DDT, to have much less unfavorable action onfoliage.

The development of DDT has been hampered, in the past, by inability toproduce the active principle, para-para DDT, in pure form without thewasteful production of large amounts of valueless byproduct. Thisobstacle is completely removed by the present invention, since 40 topercent of the active principle may be recovered in pure form while theremainder is still a standard product.

Cther modifications of my process which fall within the scope of thefollowing claims will be immediately evident to those skilled in theart.

What I claim is:

1. In the manufacture of DDT the process which comprises condensingchloral and chlorobenzene in the presence of fuming sulfuric acid andfrom about 5 to percent by weight based on the chloral employed of acatalytic agent selected from a class consisting of aromaticpolysulfonic acids, containing from 2 to 4 sulfonic acid groups, whichare soluble in but substantial- 1y non-reactive with the components ofthe reaction mixtures, cooling and agitating the resulting mixtureWithin the range of from about 10 to +25 C. while slowly adding oleumand separating the resultin DDT from the reaction

1. IN THE MANUFACTURE OF DDT THE PROCESS WHICH COMPRISES CONDENSINGCHLORAL AND CHLOROBENZENE IN THE PRESENCE OF FUMING SULFURIC ACID ANDFROM ABOUT 5 TO 60 PERCENT BY WEIGHT BASED ON THE CHLORAL EMPLOYED OF ACATALYTIC AGENT SELECTED FROM A CLASS CONSISTING OF AROMATICPOLYSULFONIC ACIDS, CONTAINING FROM 2 TO 4 SULFONIC ACID GROUPS, WHICHARE SOLUBLE IN BUT SUBSTANTIALLY NON-REACTIVE WITH THE COMPONENTS OF THEREACTION MIXTURES, COOLING AND AGITATING THE RESULTING MIXTURE WITHINTHE RANGE OF FROM ABOUT -10* TO +25* C. WHILE SLOWLY ADDING OLEUM ANDSEPARATING THE RESULTING DDT FROM THE REACTION MIXTURE; AND OLEUMCONTAINING SUFFICIENT FREE SO3 TO SUPPLY FROM ABOUT 0.5 TO 1.3 MOLES OFFREE SO3 PER MOLE OF CHLORAL TO THE REACTION MIXTURE IN ADDITION TO ANYREQUIRED TO RAISE THE SULFURIC ACID CONCENTRATION TO 100 PERCENT;SUFFICIENT CHLOROBENZENE BEING USED TO SUPPLY A TOTAL OF FROM ABOUT 2.2TO 4 MOLES CHLOROBENZENE PER MOLE OF CHLORAL.